The present invention relates to a methacrylic copolymer as a novel compound and a dispersant for pigments used in non-aqueous paints and varnishes comprising the copolymer.
The non-aqueous paints and varnishes comprise a pigment. The pigments should uniformly be dispersed within the paints and varnishes in order to ensure the formation of coated films free of any mottle. There has been known a method in which a polymer is added to paints and varnishes as a means for ensuring uniform dispersion of a pigment therein. Examples of such methods include those comprising incorporating an urethane compound carrying an amino group into paints and varnishes as disclosed in Japanese Patent Provisional Publication Nos. 62-70459, 1-135526 and 1-139132; methods comprising adding, to paints and varnishes, an isocyanate-modified acrylic polymer as disclosed in Japanese Patent Provisional Publication Nos. 63-51487 and 62-81459; and a method comprising adding, to paints and varnishes, a phosphoric acid ester derivative as disclosed in Japanese Patent Provisional Publication Nos. 63-51469.
However, the foregoing polymers are simply effective for a part of pigments and accordingly, it takes a long period of time for uniformly dispersing a pigment, in particular, carbon black having strong cohesion. When paints and varnishes comprising carbon black are stored over a long period of time, the pigment dispersed therein may sometimes cause reaggregation. For this reason, the resulting coated film may sometimes suffer from problems of mottle and reduced gloss.